A known typical voice coil actuator comprises a coil assembly and a magnet assembly. The magnet assembly comprises inner and outer yokes of magnetic flux conductive material which together define an air gap in which the coil assembly is suspended for movement within the air gap. A radially oriented magnet is sandwiched between the inner and outer yokes such that a first face of a first magnetic polarity is adjacent the inner yoke and a second face of a second opposite magnetic polarity is adjacent the outer yoke. For example, the use of a radially oriented magnet is shown in GB 670,027.
Such actuators may suffer from a large degree of flux leakage from the radial magnet. This makes the actuator unsuitable for some applications, particularly those in which the actuator is mounted close to a display used with a cathode ray tube. Furthermore, since a significant proportion of the magnetic flux is diverted from the air-gap, the magnet assembly size needs to be increased to ensure there is sufficient flux density in the air-gap to produce the necessary movement on the coil.